The present invention relates to a cationic deproteinized natural rubber latex and, more particularly, to a cationic deproteinized natural rubber latex suited to bond papers, fibers, cloths and hides, and a method of preparing the same.
Heretofore, natural rubber adhesives wherein the concentration of the rubber contained in a natural rubber latex is concentrated to about 60% have widely been used to bond papers, fibers, cloths and hides.
However, the natural rubber latex contains a protein as a non-rubber component other than the rubber component and the kind and amount of the protein vary depending on the producing district and producing season. Therefore, there arise problems such as scatter in quality and vulcanization characteristics of natural rubber adhesives as well as deterioration of qualities of natural rubber adhesives, for example, mechanical characteristics such as creep characteristics and aging resistance, and electrical characteristics such as insulating properties. There also arise problems that ammonia as a preservative is incorporated in the natural rubber latex to cause a strong odor.
Also there has recently been reported the case where a strong I type allergic symptom is caused by a protein in a natural rubber when using a natural rubber product.
A trial of solving these problems has been made by a method of efficiently removing a protein from a natural rubber latex disclosed in Japanese Published Unexamined patent (Kokai Tokkyo Koho Hei) Nos. 6-56904, 6-56905 and 6-56906. Such a method is capable of removing a protein by adding a proteolytic enzyme (protease) and an anionic or nonionic surfactant are added to a natural rubber latex, thereby to decompose a protein, and then a creamy rubber component is separated by a purification treatment such as centrifugation to remove the protein.
However, the surfactant used in the method of the publications described above is anionic or nonionic and rubber particles in the deproteinized natural rubber latex are negatively charged or in the state free from polarity.
Accordingly, it was not preferable to use, as an adhesive, such deproteinized natural rubber latex in the fibers or papers which are negatively charged when treated in water.
On the other hand, a cationic natural rubber latex incorporated with cetyltrimethylammonium bromide (CTAB) as a cationic surfactant is described in pages 94 to 95 of xe2x80x9cNatural Rubber Science and Technologyxe2x80x9d (edited by A. D. Roberts, published by Oxford University Publication, 1988). As described in such a reference document, when a sufficient amount of the cat ionic surfactant is added to the natural rubber, a latex comprising rubber particles having cations can be obtained. The latex is made cationic in such way, thereby making it possible to improve the close adhesion with the fibers or papers which are negatively charged when treated in water.
However, the natural rubber latex disclosed in the reference documents described above has such a problem that the thickness of an adhesive layer formed by the rubber latex is liable to be decreased to obtain poor bonding strength when coated the adherend with the natural rubber latex, because the concentration of the rubber component is low such as about 30% by weight.
Furthermore, the latex obtained by merely incorporating the cationic surfactant in the natural rubber latex has a problem such as poor workability on coating because of large increase in viscosity with a lapse of time and fear of a solidification action.
Also in such a case, applications of the latex are limited because its use as a natural rubber adhesive is not preferable.
Thus, an object of the present invention is to provide a cationic deproteinized natural rubber latex which can maintain excellent storage stability and workability on coating even if the concentration of the rubber component is high, and which exhibits excellent adhesion to papers, cloths and hides and also has high safety to the human body.
Another object of the present invention is to provide a treating agent for obtaining a cationic deproteinized natural rubber latex which can maintain excellent storage stability and workability on coating even if the concentration of the rubber component is high, and which exhibits excellent adhesion to papers, cloths and hides and also has high safety to the human body.
The present inventors have intensively studied to solve the problems described above and found such a novel finding that, when rubber particles in the natural rubber latex subjected to the deproteinization treatment are positively charged, the viscosity can be reduced to a sufficiently low value even if the solid content concentration of the rubber particles is increased, thus obtaining a natural rubber latex which has excellent workability on coating for adhesive and has excellent adhesion to papers, fibers, cloths and hides. Thus, the present invention has been completed.
The cationic deproteinized natural rubber latex rubber particles of the present invention is characterized in that rubber particles are positively charged and the concentration of said rubber particles is from 40 to 65% by weight and that the viscosity at 25xc2x0 C. (hereinafter referred merely to as xe2x80x9cviscosityxe2x80x9d) of the latex is 200 mPaxc2x7s or less.
According to the cationic deproteinized natural rubber latex of the present invention, since the viscosity of the latex is maintained at a low value such as 200 mPaxc2x7s or less even if the concentration of the rubber particles (concentration of the rubber component in the latex) is a high value ranging from 40 to 65%, the workability on coating is good and an adhesive layer having a uniform thickness can be formed in case of coating the adherend. Accordingly, neither poor thickness nor unevenness does occur when the adhesive layer is formed, thereby making it possible to obtain a sufficient bonding strength.
The cationic deproteinized natural rubber latex according of the present invention is prepared by subjecting to a deproteinization treatment using a proteolytic enzyme and one or more surfactants selected from cationic and nonionic surfactants, and contains both cationic and nonionic surfactants after the treatment.
That is the cationic deproteinized natural rubber latex is characterized in that a protein in the natural rubber latex is removed by the deproteinization treatment using a deproteinizing agent containing a proteolytic enzyme and cationic and/or nonionic surfactants, and the cationic surfactant and nonionic surfactant finally coexists in the latex.
According to the cationic deproteinized natural rubber latex of the present invention, it is made possible to obtain a latex having excellent dispersion stability and storage stability, to maintain the viscosity of the latex at 200 mPaxc2x7s or less even in case of a so-called high-concentration latex having a rubber component in a concentration of more than 40% by weight, and to sufficiently prevent phenomenon such as increase in viscosity with a lapse of time, solidification or cohesion.
The cationic surfactant not only contributes to an improvement in dispersion stability and storage stability of the latex, but also exerts an action of making the latex cationic, i.e. an action of positively charge the rubber particles in the latex to form a suspension of the cation charged particles in water. As a result, the latex of the present invention exhibits excellent adhesion to papers, fibers, cloths and hides.
According to the effects described above, the cationic deproteinized natural rubber latex of the present invention exhibits excellent adhesion and excellent workability on coating for a base latex in a natural rubber adhesive suited to bond to papers, fibers, cloths and hides.
In the present invention, the protein contained in the natural rubber latex as the raw material is removed by the deproteinization treatment. As a result, the latex of the present invention prevents allergy caused by the protein and therefore has high safety to the human body.
The method of preparing a cationic deproteinized natural rubber latex of the present invention is characterized by subjecting a natural rubber latex to a deproteinization treatment using a proteolytic enzyme and one or more surfactant selected from cationic and nonionic surfactants, concentrating the deproteinized latex so that the concentration of a rubber component in the latex is within a range from 40 to 65% by weight, and incorporating at least the surfactant which was not incorporated on the deproteinization treatment among the cationic surfactant and nonionic surfactant.
According to the method of preparing a cationic deproteinized natural rubber latex of the present invention, there can be obtained a cationic deproteinized natural rubber latex which maintains the viscosity at 200 mPaxc2x7s or less even if the concentration of the rubber component is high such as 40 to 65% by weight, and which prevents an increase in viscosity with a lapse of time of the latex and also exhibits excellent storage stability.
The treating agent for cationic deproteinized natural rubber latex of the present invention is used to treat the natural rubber latex as the raw material so as to obtain the cationic deproteinized natural rubber latex of the present invention, and it includes:
(1) a treating agent for cationic deproteinized natural rubber latex, comprising (A) a deproteinizing agent containing at least a proteolytic enzyme and one or more cationic surfactants as an active component, and (B) an additive containing at least one or more nonionic surfactants as an active component which is added after treatment according to said deproteinizing agent;
(2) a treating agent for cationic deproteinized natural rubber latex, comprising (A) a deproteinizing agent containing at least a proteolytic enzyme and one or more nonionic surfactants as an active component, and (C) an additive containing at least one or more cationic surfactants as an active component which is added after treatment of said deproteinizing agent; or
(3) a treating agent for cationic deproteinized natural rubber latex, comprising at least a proteolytic enzyme, one or more cationic surfactants and one or more nonionic surfactants as an active component.
According to the treating agent of the present invention, it is made possible to positively charge rubber particles in the latex and to maintain the viscosity of the latex at a low viscosity such as 200 mPaxc2x7s or less even if the concentration of the rubber component is adjusted to high concentration such as 40 to 65% by weight, thus making it possible to obtain a cationic deproteinized natural rubber latex which prevents an increase in viscosity with a lapse of time of the latex and also exhibits excellent storage stability.
The present invention will be described in detail below.
The cationic deproteinized natural rubber latex of the present invention is a deproteinized natural rubber latex comprising cationic rubber particles, which is adjusted so that the viscosity of the latex is 200 mPaxc2x7s or less when the concentration of the rubber component is within a range from 40 to 65% by weight.
Cationic latex, i.e. positively charged rubber particles in the latex increases the affinity for papers, cloths and hides which are liable to be negatively charged in water, thereby enhancing the bonding strength.
The concentration of the rubber component in the cationic deproteinized natural rubber latex of the present invention is adjusted within a range from 40 to 65% by weight to exhibit excellent workability on coating for a base latex of a natural rubber adhesive.
When the concentration of the rubber component is lower than40% by weight, it becomes impossible to obtain a sufficient bonding strength for the base latex of the adhesive when using as the natural rubber adhesive. On the other hand, when the concentration of the rubber component exceeds 65% by weight, it becomes difficult to adjust the viscosity of the latex to 200 mPaxc2x7s or less, thereby causing such problems that the workability on coating is lowered when using as the natural rubber adhesive, or the dispersion stability and storage stability of the latex are lowered.
The concentration of the rubber component is preferably from 45 to 65% by weight, and more preferably from 45 to 60% by weight, within the range described above.
(Physical properties of cationic deproteinized natural rubber latex)
The viscosity of the latex is 200 mPaxc2x7s or less, preferably 100 mPaxc2x7s or less, and more preferably within a range from 20 to 100 mPaxc2x7s or less, when the concentration of the rubber component is within a range from 40 to 65% by weight.
The upper limit of the viscosity must be maintained until coating. When the viscosity of the latex on coating exceeds 200 mPaxc2x7s, the workability on coating is lowered. In this case, since formation of bubbles in the latex is accelerated, a uniform adhesive layer can not be obtained, thus causing problems such as lowering of the bonding strength. The lower limit of the viscosity is not specifically limited, and may be appropriately adjusted as far as it is free from such a problem that the workability on coating is lowered because of too high fluidity of the latex.
As the latex which is a starting material to obtain the cationic deproteinized natural rubber latex of the present invention, there can be used conventionally known various natural rubber latexes such as ammonia-retaining concentrated natural rubber latex (concentration of rubber component: about 60%) and field latex (concentration of rubber component: about 30%) collected from rubber trees.
In case the cationic deproteinized natural rubber latex of the present invention is prepared, as described herein after, a natural rubber latex as the starting material is subjected to a deproteinization treatment composed of a treatment of decomposing a protein and a treatment of purifying by removing a non-rubber component such as decomposed protein.
The proteolytic enzyme used to subject the natural rubber latex to a deproteinization treatment is not specifically limited and a conventionally known one can be used, and examples thereof include alkaline protease. The protease may be derived from any of bacteria, filamentous bacteria and yeast, and the protease is preferably derived from bacteria, particularly preferably from the genus Bacillus. It is also possible to use enzymes such as lipase, esterase, amylase, lacase and cellulase in combination.
As the proteolytic enzyme used in the present invention, or example, protease KAP having a resistance to the surfactant manufactured by Kao Corp. is used particularly preferably among the enzymes described above.
When using alkaline protease as the proteolytic enzyme, its activity [measured value obtained by modification of the Anson-hemoglobin method (Anson. M. L. J. Gen. Physiol., 22, 79(1938)] is within a range from 0.1 to 50 APU/g, and preferably within a range from 1 to 25 APU/g.
The amount of the proteolytic enzyme to be added is preferably set within a range from 0.0001 to 20 parts by weight, and more preferably within a range from 0.001 to 10 parts by weight, based on 100 parts by weight of the rubber component of the natural rubber latex. When the amount of the proteolytic enzyme is within the range described above, a protein in the latex can be sufficiently decomposed and the activity of the enzyme is retained, thereby making it possible to effectively exert the effect corresponding to the addition. Therefore, it is advantageous in view of the cost. In case the enzyme is added, pH adjustors such as disodium hydrogen phosphate and other additives may be added.
In case the cationic deproteinized natural rubber latex of the present invention is prepared,
(i) for the purpose of stably dispersing a rubber component in a latex on decomposition of a protein, and
(ii) for the purpose of improving the dispersion stability and storage stability of the latex and positively charging rubber particles in the latex to form a suspension of cation charged particles in water, one or more cationic surfactants and one or more nonionic surfactants as a stabilizer are used in the latex.
Examples of the cationic surfactant used in the present invention include alkylamine salt, alkylamine derivative and quaternized compound thereof.
Examples of the alkylamine salt include, but are not limited to, salts of primary amine, secondary amine and tertiary amine. Examples of the salt include hydrochloride, phsophate, actate, alkyl sulfate, alkylbenzenesulfonic acid, alkylnaphthalenesulfonic acid, fatty acid, organic acid, alkyl phosphate,alkyl ether carboxylic acid, alkylamide ether carboxylic acid, anionic oligomer, and anionic polymer.
The alkylamine derivative has at least one of an ester group, an ether group and an amide group in a molecule and examples thereof include polyoxyalkylene (AO) alkylamine and a salt thereof, alkyl ester amine (including AO adduct) and a salt thereof, alkyl ether amine (including AO adduct) and a salt thereof, alklyamideamine (including AO adduct) and a salt thereof, alkyl ester amideamine (including AO adduct) and a salt thereof, and alkyl ether amideamine (including AO adduct) and a salt thereof. Examples of the salt include hydrochloride, phosphate, acetate, alkyl sulfate, alkylbenzenesulfonic acid, alkylnaphthaleensulfonic acid, fatty acid, organic acid, alkyl phosphate, alkyl ether carboxylic acid, alkylamide ether carboxylic acid, anionic oligomer, and anionic polymer.
Specific examples of the acetate include coconutamine acetate and stearylamine acetate.
The alkyl group in the alkylamine salt and alkylamine derivative usually includes, but is not limited to, straight-chain, branched or Guerbet-shaped alkyl groups having 8 to 22 carbon atoms
Examples of the quaternized compound of the alkylamine salt and alkylamine derivative include those prepared by quaternizing the alkylamine salt and alkylamine derivative with methyl chloride, methyl bromide, or dimethylsulfuric acid.
The quaternary ammonium salt includes, for example, those having a C8-22 alkyl group and, more specifically, it includes, for example, alkyltrimethylammonium halide such as lauryltrimethylammonium halide, cetyltrimethylammonium halide, or stearyltrimethylammonium halide; dialkydimethylammonium halide such as distearyldimethylammonium halide; trialkylmethylammdnium halide; dialkylbenzylmethylammonium halide; or alkylbenzyldimethylammonium halide.
Among the cationic surfactants described above, cetyltrimethylammonium chloride (CTAC) and stearyltrimethylammonium chloride are preferably used in the present invention because of particularly excellent effect of stabilizing the latex.
The content of the cationic surfactant is set in both of a deproteinizing step described hereinafter and a subsequent post-adding step so that the content of the cationic surfactant can be adjusted within a range from 0.5 to 20% by weight based on the rubber component of the latex.
When the content of the cationic surfactant is within the above range, the cationic surfactant is sufficiently adsorbed in the rubber particles of the latex and low moisture-absorption properties of the solid rubber is retained on drying of the latex, thereby making it, possible to effectively exert the effect corresponding to the amount. Therefore, it is advantageous in view of the cost.
The nonionic surfactant used in the present invention includes, for example, polyoxyalkylene ether surfactant, polyoxyalkylene ester surfactant, polyhydric alcohol fatty ester surfactant, saccharide fatty ester surfactant, or alkyl polyglycoside surfactant.
The polyoxyalkylene ether surfactant includes, for example, polyoxyalkylene alkyl ether, polyoxyalkylene alkyl phenyl ether, polyoxyalkylene polyol alkyl ether, or polyoxyalkylene mono-, di- or tristyryl phenyl ether. The polyol includes, for example, polyhydric alcohols having 2 to 12 carbon atoms, such as propylene glycol, glycerin, sorbitol, glucose, sucrose, pentaerythritol, and sorbitan.
The polyoxyalkylene ester surfactant includes, for example, polyoxyalkylene fatty ester or polyoxyalkylene alkyl rosinate.
The polyhydric alcohol fatty ester surfactant includes, for example, fatty ester of polyhydric alcohol having 2 to 12 carbon atoms, or fatty ester of polyoxyalkylene polyhydric alcohol. More specifically, it includes sorbitol fatty ester, sorbitanfattyester, glycerinfattyester, polyglycerinfatty ester, or pentaerythritol fatty ester. In addition, polyalkylene oxide adducts thereof (e.g. polyoxyalkylene sorbitan fatty ester, polyoxyalkylene glycerin fatty ester, etc.) can also be used.
The saccharide fatty ester surfactant includes, for example, fatty acid esters of sucrose, glucose, maltose, fructose, and polysaccharides. In addition, polyalkylene oxide adducts thereof can also be used.
The alkyl polyglycoside surfactant includes, for example, alkyl glucoside, alkyl polyglucoside, polyoxyalkylene alkyl glucoside, polyoxyalkylene alkyl polyglucoside, or fatty acid esters thereof. In addition, polyalkylene oxide adducts thereof can also be used.
In addition, polyoxyalkylenealkylamine or alkylalkanolamide can be used.
The alkyl group in the nonionic surfactant includes alkyl groups having 4 to 30 carbon atoms. The polyoxyalkylene group includes those having a C2-4 alkylene group, for example, those wherein the number of ethylene oxide is within a range from about 1 to 50 moles. The fatty acid includes, for example, straight-chain or branched, saturated or unsaturated fatty acids having 4 to 30 carbon atoms.
Among the nonionic surfactants described above, the polyoxyalkylene ether surfactant such as polyoxylene alkyl phenyl ether having a large effect of stabilizing the latex is preferable, and those having a hydrophile-lipophile balance (HLB) of 10 or more are more preferable because of a large effect of enhancing the storage stability of the latex.
The content of the nonionic surfactant is set in both of a deproteinizing step described hereinafter and a subsequent post-adding step so that the content of the nonionic surfactant can be adjusted within a range from 0.2 to 5.0% by weight based on the rubber component of the latex.
When the content of the nonionic surfactant is within the above range, it is more preferable to the effect of enhancing the storage stability of the latex and the effect of the cationic surfactant adsorbed in the rubber particles of the latex can be sufficiently maintained.
Use of those other than the surfactants described above, i.e. anionic and amphoteric surfactants, in the present invention exerts an action of eliminating the effect of the present invention obtained by adding the cationic surfactant. Accordingly, it is preferable that the cationic deproteinized natural rubber latex of the present invention substantially contains neither an anionic surfactant nor an amphoteric surfactant.
The cationic deproteinized natural rubber latex of the present invention of the present invention is preferably used as an adhesive for papers, fibers, cloths and hides, for example, as it is or after subjecting rubber molecules in the latex to a graft modification treatment.
The cationic deproteinized natural rubber latex of the present invention is prepared by passing through the following steps of:
(1) optionally diluting a natural rubber latex with water, adding a proteolytic enzyme and one or more cationic surfactants or one or more nonionic surfactants as a stabilizer, thereby to decompose a protein, followed by removal of a non-rubber component and further purification (deproteinizing step), and
(2) incorporating, as a stabilizer, at least the surfactant which was not incorporated on the deproteinization treatment among the cationic surfactant and nonionic surfactant to a cream component concentrated by the purification treatment, and optionally adding an antioxidant (post-adding step), or by passing through the step of:
(1xe2x80x2) optionally diluting a natural rubber latex with water, adding a proteolytic enzyme and one or more cationic surfactants and one or more nonionic surfactants as a stabilizer, thereby to decompose a protein, followed by removal of a non-rubber component and further purification (deproteinizing step).
In the deproteinizing steps (1) and (1xe2x80x2)described above, the concentration of the rubber component is reduced by optionally diluting the natural rubber latex as a raw material with water, and then the natural rubber latex is matured by adding, the proteolytic enzyme, one or more cationic surfactants and/or one or more nonionic surfactants, whereby the deproteinizing treatment proceeds.
Since protein bonded or adsorbed to the rubber particles, thereby to stabilize them, is decomposed with this treatment to a low-molecular one, the treated protein is possible to be easily transferred to a water layer.
On the other hand, the surfactant is adsorbed to the rubber particles in place of the protein, thereby stabilizing the latex.
The concentration of the rubber component on deproteinization treatment is not specifically limited, but the rubber component is diluted to reduce the content within a range from 5 to 40% by weight, and preferably from 10 to 30% by weight, so as to exert the effect of the deproteinization treatment as possible.
The conditions of the deproteinization are not specifically limited, but the deproteinization treatment is usually conducted at a temperature within a range from 5 to 90xc2x0 C., and preferably from 20 to 60xc2x0 C., for about several minutes to one week.
In the removal of the non-rubber component and purification which are subsequently conducted after the deproteinization treatment, the latex is concentrated by centrifugation or ultrafiltration and the non-rubber component transferred in water such as protein decomposition product is removed to purify the latex.
In case the latex is concentrated by centrifugation, the latex is centrifuged at 5000 to 10000 rpm (centrifugal force at a gravity acceleration of about 9000 G) for about 1 to 60 minutes and a cream component obtained by concentrating the rubber component may be removed. In this case, the latex may be continuously separated by using a disc type centrifugal separator. The purification of the latex may be repeated, if necessary.
In the present invention, the step of further incorporating a surfactant to the cream component obtained by the purification, i.e. a rubber component of the deproteinized latex, is conducted.
In such a step, the nonionic surfactant may be incorporated when using the cationic surfactant alone in the deproteinizing step (1), while the cationic surfactant may be incorporated when using the nonionic surfactant alone in the deproteinizing step (1). When using the cationic surfactant in combination with the nonionic surfactant in the deproteinizing step, the cationic and/or nonionic surfactants can be post-added furthermore.
In any of the deproteinizing step (1) and post-adding step (2), the amount of the cationic surfactant and nonionic surfactant may be adjusted so that the content of the surfactant based on the rubber component of the latex respectively satisfies the range described above.
It is not necessary to incorporate the surfactant, which has already been incorporated in the deproteinizing step, in the post-adding step (2). However, since the content of the already-incorporated surfactant is commonly reduced after passing through the deproteinizing and purifying processes, the surfactant may be added again as far as the content based on the rubber component of the latex satisfies the range describe above.
The method of incorporating the surfactant in the post-adding step of the surfactant is not specifically limited, but an aqueous solution prepared by diluting the surfactant in a concentration of 10 to 20% by weight is preferably added while stirring the latex.
The treating agent of the present invention is used in the preparation of the cationic deproteinized natural rubber of the present invention, and includes the followings:
a treating agent comprising a deproteinizing agent used in the deproteinizing step (1) and a post additive used in the post-adding step, and
a treating agent used in the deproteinizing step (1xe2x80x2).
Among the treating agents in the present invention, the treating agent comprising a deproteinizing agent and a post additive is further classified into two types:
(I) a treating agent comprising a deproteinizing agent containing at least a proteolytic enzyme and at least one cationic surfactant as an active component and a post additive containing at least one nonionic surfactant as an active component, and
(II) a treating agent comprising a deproteinizing agent containing at least a proteolytic enzyme and at least one nonionic surfactant as an active component and a post additive containing at least one cationic surfactant as an active component.
According to the treating agent (I), since the deproteinizing agent contains the proteolytic enzyme, the protein in the natural rubber latex can be decomposed by using such a deproteinizing agent. Since the deproteinizing agent contains the cationic surfactant, the latex is subjected to a deproteinization treatment using a deproteinizing agent, thereby making it possible to provide the latex with the cationic properties and to stabilize the latex. Furthermore, since the post additive contains the nonionic surfactant, use of both the cationic and nonionic surfactants in combination can be realized in the post-adding step and the latex is further stabilized without impairing the cationic properties of the latex, thereby making it possible to exert excellent storage stability.
According to the treating agent (II), since the deproteinizing agent contains the proteolytic enzyme, the protein in the natural rubber latex can be decomposed by using such a deproteinizing agent. Since the deproteinizing agent contains the nonionic surfactant, the latex can be stabilized when the latex is subjected to a deproteinization treatment using a deproteinizing agent. Furthermore, since the post additive contains the cationic surfactant, the latex can be provided with the cationic properties and use of both the cationic and nonionic surfactants in combination can be realized in the post-adding step. Furthermore, the latex is further stabilized, thereby making it possible to exert excellent storage stability. Accordingly, there can be obtained a cationic deproteinized natural rubber latex which prevents an increase in viscosity during the storage even when using any of the treating agents described above, and which maintains the viscosity at 200 mPaxc2x7s or less even if the concentration of the rubber component is high such as 40 to 65% by weight.
Since the treating agent used in the deproteinizing step (1xe2x80x2) described above contains the proteolytic enzyme, cationic surfactant and nonionic surfactant, such a treating agent makes it possible to deproteinize the natural rubber latex, to stabilize the latex on the deproteinization treatment and to provide the latex with the cationic properties, simultaneously.
The proteolytic enzyme, cationic surfactant and nonionic surfactant to be used in the treating agent of the present invention are the same as those described above.
The content of the proteolytic enzyme, cationic surfactant and nonionic surfactant in the treating agent of the present invention may be appropriately set so that the content of each component based on the rubber component in the latex satisfies the range described above when the treating agent is incorporating in the natural rubber latex.